The present invention relates to a novel alkaline protease, a method for preparing the novel alkaline protease and a novel alkalophilic actinomycete strain having an ability of producing the alkaline protease.
The alkaline protease is an enzyme which can specifically hydrolyze the peptide bond of proteins under an alkaline condition and has widely been used in various industrial fields such as food, textile, leather and detergent industries. It has been known that such alkaline proteases are produced by a wide variety of microorganisms such as filamentous fungi, yeast and bacteria and are also produced by a group of microorganisms which belong to the so-called alkalophilic microorganisms.
As alkaline proteases produced by the foregoing alkalophilic microorganisms, there have already been known a lot of enzymes such as those produced by so-called alkalophilic Bacillus (see, for instance, Japanese Examined Patent Publication (hereinafter referred to as "J. P. KOKOKU") No. Hei 7-63366, J. P. KOKOKU Nos. Hei 7-63367 and Hei 7-63368) and these enzymes have been developed for use principally in detergents. In addition, there have also been known, for instance, an alkaline protease produced by the strain AH-101 (Japanese Un-Examined Patent Publication (hereinafter referred to as "J. P. KOKAI") No. Hei 2-255087) and an alkaline protease produced by the strain B18-1 (J. P. KOKOKU No. Hei 7-63368), as heat-stable enzymes produced by strains belonging to the genus alkalophilic Bacillus similar to the foregoing. However, there has not widely been known proteases produced by strains belonging to the alkalophilic actinomycetes which fall within the scope of alkalophilic microorganisms and there has been reported only a limited number of enzymes such as those derived from strains belonging to the genus alkalophilic Streptomyces (Agr. Biol. Chem., 1974, 38(1), pp. 37-44) and an alkaline protease produced by the strain HS682 belonging to the genus alkalophilic Thermoactinomyces (Biosci. Biotech. Biochem., 1992, 56(2), pp. 246-250).
On the other hand, when applying proteases to detergents, it has been indicated that the enzyme should act even on insoluble proteins such as keratin (M. Minagawa, SENSHO-SHI, 1985, 26, p. 322). In this case, it is needless to say that the enzyme should also intensively decompose soluble proteins such as casein. In Addition, if proteases are incorporated into detergents for bathtubs, drainage canals of bath floors and drains for dressing and washing stands, the enzymes used must maintain their activities at a moderate temperature of about 40.degree. C. and must have an ability to intensively decompose keratin such as hairs and the dirts. The detergents and washing agents which are presently put on the market have a pH falling within an alkaline region because of their compositions and therefore, the optimum enzyme to be incorporated into these detergents and washing agents is an alkaline protease.
Moreover, hairs and feathers comprising keratin as a principal protein component are important as raw materials for preparing cysteine whose chemical synthesis is impossible. Cysteine has presently been prepared by hydrolyze hairs or the like under acidic conditions, i.e., through a chemical reaction. However, the acid-hydrolysis requires the use of severe reaction conditions and a large amount of the resulting cysteine is decomposed and this results in a quite low yield. For this reason, there has been desired for the use of mild hydrolysis such as a treatment with a protease. In this case, the enzyme as a hydrolytic agent is most preferably an alkaline protease since keratin is liable to get swollen and to be susceptible to the action of an enzyme, in a highly alkaline region.
There have been proposed the use of the alkaline protease produced by the foregoing strain AH-101 and those produced by strains belonging to the genus alkalophilic Streptomyces, for these applications. However, these enzymes are still insufficient for putting into practical use because of their low ability to decompose, in particular, keratin. Accordingly, there has been desired for the development of a novel alkaline protease possessing a higher ability to decompose proteins, in particular, keratin.